1. Field of the Invention
The present invention relates to a differential current driving type transmission and reception system, and more particularly, to differential current driving type transmitter and receiver which transmits and receives data in the direction of current flowing through transmission lines and a differential current driving type interface system having the transmitter and receiver.
2. Description of the Related Art
In general, a transmission-side semiconductor chip is configured to transmit voltage type signals through a unit transmission line or a pair of differential transmission lines, and a reception-side semiconductor chip is configured to sense the signals transmitted in the voltage type. In particular, in the case of the differential voltages transmitted through the pair of differential transmission lines, data is recognized using a voltage difference between the signals transmitted through two differential transmission lines. This method can be influenced by the electrical characteristics of the differential transmission lines which connect the semiconductor chips. Recently, the distance between semiconductor chips is gradually increased, and, in some new transmission methods, transmission lines have substantial impedance. Accordingly, since a time constant of a signal that is determined by the impedance of transmission lines and the capacitance between the transmission lines and a board increases, it is difficult to transmit and receive data within a short period. For this reason, the data transmission method using a voltage difference has proved inappropriate, and a current driving method for transmitting and receiving data using current has been suggested in the art.
In the current driving method, since data to be conveyed is transmitted in the type of current, a receiver restores the data from the signal transmitted in the type of current and uses restored data. The current driving method is divided into a single current driving method in which one data bit is transmitted through one transmission line, and a differential current driving method in which currents having different magnitudes are transmitted through two transmission lines and data is restored using a current difference between the two transmission lines.
In the differential current driving method, a transmitter generates currents of different magnitudes which correspond to data to be transmitted and transmits the currents through two transmission lines, and a receiver restores the data using a current difference between the currents flowing through the two transmission lines. In the differential current driving method, when compared to the single current driving method, while the distortion of transmitted signals by noise is not substantial, interference occurs between the transmission lines due to the physical positions of the two transmission lines and the parasitic resistance, parasitic inductance and parasitic capacitance of the two transmission lines.
Although two differential currents flowing from the transmitter to the receiver are based on the assumption that two current sources used for generating the two differential currents source or sink the same current value, in practice, different current values can result due to process deviations. Also, when the currents which are sourced or sunk by current sources disposed in the receiver are distorted by the noise introduced through the transmission lines, the qualities of differential current signals are degraded. Summarizing this, the transmitted signals are likely to be distorted due to interference between the two transmission lines, and the time constants of the transmission lines increase to lengthen the transient times of the signals, whereby the transmission speeds of the signals cannot but increase.
FIG. 1 is a view showing signals of a trueline, which are outputted from a transmitter of a conventional differential current driving system.
Referring to FIG. 1, when the current sources for generating the two differential currents produce current values of different magnitudes due to the above-described reasons, it is to be appreciated that the magnitudes shift by a preset deviation a, that is, an offset, each time when the directions of the currents applied to the truelines are changed.
The conventional differential current driving method and the system for realizing the method are unstable because they have the above-described problems. Therefore, novel data transmission and reception methods free from these problems are keenly demanded in the art.